This invention relates to the consolidation of filamentary glassy metallic alloys under heat and pressure by uniaxial pressing to form discrete self-supporting glassy metallic alloy bodies of substantially uniform composition.
Glassy metallic alloys, also commonly referred to as amorphous metallic alloys, do not exhibit the regular atomic structural periodicity of metals in the crystalline state. Glassy metallic alloys, therefore, in contrast to crystalline metals, do not exhibit well-defined peaks during X-ray diffraction measurements. From such diffraction measurements, however, it has been determined that amorphous metals have no long range structure and, in that respect, their atomic structures closely resemble those of the precursor liquid state.
Glassy metallic alloys generally possess physical properties such as hardness and strength far in excess of their crystalline counterparts. The magnetic properties of magnetic glassy metallic alloys generally also differ from those of their crystalline counterparts and are of considerable interest to manufacturers of electrical equipment. Since glassy magnetic metals, unlike normal crystalline magnetic metals, have no long range atomic order in their structure, the directionality of properties such as magnetization normally associated with crystal anisotropy is absent. Also, unlike normal metals, glassy metals are extremely homogeneous, being devoid of compositional heterogeneity, inclusions and structural defects. The lack of magnetic directionality gives metallic glasses good d-c magnetic properties including extremely low field requirements for saturation which allows magnetization reversal at extremely low fields (i.e., a low coercive field). Magnetic materials having low coercive field and low field requirements for saturation, i.e., high permeability, are commonly referred to as magnetically soft. Typical sofe magnetic glassy metallic alloys in ribbon form are disclosed in U.S. Pat. No. 4,038,073 to O'Handley et al. which is herein incorporated by reference in its entirety.
Amorphous structures can be obtained by several techniques. Electroplating, vapor deposition, and sputtering are all techniques where the material is deposited on an atom-by-atom basis. Under appropriate conditions, the atoms are "frozen" in-situ on contact and usually cannot diffuse into the lower energy configurations associated with a more stable lattice. The resulting metastable structure is a non-crystalline glassy one. These processing methods, however are not economically feasible for producing large commercial quantities.
Another method for producing glassy structures in some metals is by cooling rapidly from the liquid melt. Two major conditions apply in achieving the glassy structure by this method. First, the composition should be selected to have a high glass transition temperature, T.sub.g, and a low melting temperature, T.sub.m. Specifically, the T.sub.g /T.sub.m ratio should be as large as possible. Second, the liquid should be cooled as rapidly as possible from above T.sub.m to below T.sub.g. In practice, it is found that to produce metallic glasses, the cooling rate must be rapid enough, i.e., on the order of a million degrees centigrade per second, to circumvent crystallization which would otherwise occur. Even at the high cooling rates typically used, only alloys of certain compositions can be made amorphous by quenching from the malt. One class of metallic alloys consists of "glass-forming' metalloid atoms, e.g., phosphorous, boron, silicon, and carbon as required additions; usually in the 10 to 25 atomic percent range.
One technique for obtaining the very rapid cooling rates required is chill block melt-spinning, as described in U.S. Pat. No. 4,177,856, incorporated herein by reference in its entirety. Continuous melt-quenching techniques such as melt-spinning are very attractive from a production standpoint in that large amounts of thin glassy alloy filament, tape, etc., may be cast at speeds typically up to 50 m/s. Unless special equipment is used to guide and coil the filament, it will be cast from the spinning chill block into piles having an intertwined or tangled appearance as newly formed portions of the continuous filaments fall into open areas between previously ejected portions.
Metallic glasses undergo inhomogeneous plastic deformation through the formation of highly localized shear bands at temperatures well below the glass transition temperature, T.sub.g. At temperatures well below T.sub.g, these high strength, high modulus materials have fracture stresses marginally greater than the yield stress and do not exhibit substantial elongation in tension. In contrast, the mode of plastic deformation near T.sub.g is one in which the macroscopic strain in the specimen results from homogeneous deformation by viscous-like flow throughout the entire sample volume. The "plastic" transition temperature, T.sub.p, corresponds to the changeover from one deformation mode to the other.
Discussion of the deformation behavior of glassy metallic alloys as a function of temperature appears not infrequently in the literature, e.g., Japanese Pat. No. S.53 (1978)-57170 of May 24, 1978 to T. Masumoto. In his patent, Masumoto describes the temperature regime between the crystallization temperature and the "ductile" transition temperature, in which uniform deformation easily occurs. Masumoto also proposes that forming processes such as rolling, punching, pressing, pulling out, and bending will be viable in that temperature regime; however, his examples are restricted to the rolling, pulling out and bending processes on a single ribbon and are primarily designed to demonstrate feasibility of easy deformation in the subject temperature regime.
One significant drawback to the utilization of glassy metallic alloys is that at the present time they can only be produced from the melt in large quantities in the form of filaments, ribbons, or flakes having thicknesses on the order of up to about 0.01 cm. If the processing parameters are changed to produce thicker ribbon, it is generally not possibly to also obtain the very rapid cooling rates through the entire cross section required to avoid incipient crystallization. A second drawback is that the crystallization temperature forms an upper bound on the temperature to which the alloy may be heated in attempts to form large glassy metallic shapes from glassy filaments or ribbons.
The use of binders to agglomerate ribbons or flakes described, for example, in U.S. Pat. Nos. 4,197,146 and 4,201,837 to Frischmann and Lupinski, respectively, incorporated herein by reference, does not alleviate the drawback related to the crystallization temperature of the alloy and is also subject to temperature limits based on decomposition of the binder. Also, the presence of the binder inhibits development of properties projected for 100% dense bodies since some portion of the volume is occupied or made discontinuous by the presence of the binder.
Components or bodies formed from flakes (as described in U.S. Pat. No. 4,197,146, referenced above), discontinuous ribbon segments (as described in U.S. Pat. No. 4,201,837, referenced above), and powders without binders are subject to additional costs involved in making suitable flakes, discontinuous ribbon segments and powders compared to the costs of producing ribbons. Also, although physical properties are substantially uniform along the length of ribbons, such uniformity is generally not to be found among flakes, discontinuous ribbon segments or powders. Such variations in the form of end effects are particularly to be expected where the flakes or discontinuous ribbon segments are produced from the melt on casting wheels having local lines of low conductivity which may cause the formation of lines of brittle crystalline material along which the cast material fractures to define the flakes. It has generally been observed that components formed with or without binders have poorer soft magnetic characteristics than the flakes or discontinuous ribbon segments from which they are formed.
It is, therefore, an object of this invention to provide a binderless method for the consolidation of continuous filaments of glassy metallic alloys to form dense self-supporting glassy metallic alloy bodies of substantially uniform composition.
Another object of this invention is to provide discrete self-supporting glassy metallic alloy bodies of substantially uniform composition having properties substantially the same as those of the filamentary glassy material from which they are formed.
A further object of this invention is to provide dense discrete glassy magnetic metallic bodies of substantially uniform composition having superior soft magnetic properties substantially the same as those of the filamentary glassy soft magnetic material from which they are formed.
Other objects of this invention will, in part, be obvious and will, in part, appear hereinafter.